Mastitis is a condition encompassing the infection and inflammation of the mammary glands in animals and humans. Reference throughout this specification will be made to the use of the present invention to detect mastitis in ruminants such as cows. However, it should be appreciated that the reference to cows is by way of example only and the present invention can also have application to the detection of mastitis in other animals and possibly humans.
Mastitis is an expensive disease, costing dairy farmerssignificantly whether through lower quality milk, smaller yields plus the time and expense spent treating mastitis.
There are two main stages of mastitis.
Clinical mastitis can be detected visually through observing red and swollen mammary glands and through the production of clotted milk. Once detected, farmers divert milk from mastitic cows or teats to a waste line so that it is not collected in the main milk vats during milking and therefore will not adversely affect milk quality.
Sub-clinical mastitis cannot be detected visually through either observation of the gland or the milk produced. Because of this, farmers do not have the option of diverting milk from sub-clinical mastitic cows or teats. Yet, this milk is of poorer quality than that from non-infected cows and can thus contaminate the rest of the milk in the vat.
Further, there is a lower milk yield from cows having sub-clinical mastitis, and the real likelihood that clinical mastitis will shortly develop with its associated problems including significant damage to udder tissue.
Thus, the earlier that mastitis can be detected, particularly in the sub-clinical stage the better. With less damage to the udder, there is a longer time that the cows can produce and the milk that they produce is of greater quality.
It has been estimated that sub-clinical cases of mastitis cost the industry more than clinical mastitis in terms of financial loss (Douglas et al., 1997).
Currently there are a number of ways by which mastitis is detected.
One method is initial detection by the farmer of clots on the milk filter. This can indicate to the farmer that there is mastitis in the herd.
This method of detection is obviously too late to prevent contamination of the milk vat for that day. However, the farmer can be alerted to check every teat in his/her herd, either by visually assessing if there is infection and/or squirting milk from the teat onto the milking shed floor to determine if there are clots therein.
Along with late detection in terms of the ability to divert milk, this method is also labour intensive as it involves inspection of a whole herd. Another problem is that this method does not detect sub-clinical mastitis.
Another method, used to detect mastitis is somatic cell counts. This normally involves taking a sample of milk from the cow and then sending the sample to a laboratory to be tested in a specialised and expensive cell counter machine.
This test has the advantage that it is good at detecting sub-clinical mastitis, but has the disadvantage in that the test is only undertaken at intervals usually of at least one week. In New Zealand, routine somatic cell counts are undertaken daily on a bulk milk sample from the milk vat. The presence of mastitis in the herd can be detected by a sudden increase in somatic cell concentrations but the farmer is then faced with the problem of finding the infected quarter(s) in the herd.
Another method of testing for mastitis involves testing the conductivity of the milk (Woolford et al., 1997). A conductivity test has advantages in that it can be relatively quick to obtain results and the conductivity tester may be a handheld device or in preferred uses of this method an in-line device for use in the milking machine. In this case, mastitic milk can be detected and diverted from the main milk vat.
A further advantage of this method is that the infected cow can be detected by the milking machine at the time of milking, allowing for the cow to be treated for mastitis while still in the milking shed.
However, there are problems associated with this test. For example, the present methods of measuring conductivity give a large number of false positives and false negatives.
Further, the conductivity of milk changes during the milking process along with the fat proportion. Thus, at any one time the conductivity measure is not necessarily measuring representative samples.
Another complication is that cows on heat have a different level of conductivity in their milk than other cows.
Yet another problem is that conductivity has not been shown as being sufficiently sensitive to determine sub-clinical mastitis.
It is an object of the present invention to address the foregoing problems or at least to provide the public with a useful choice.
Further aspects and advantages of the present invention will become apparent from the ensuing description which is given by way of example only.